To answer Max's question for everyone :
Chris ( latemodel21 ) send me a 65mm SRT6 alternator pulley to try.
I didn't have a impact wrench short enough to fit and remove the 24 mm pulley nut with the alternator in place, so I removed it.

Turned out that the SRT6 pulley would not work due to a small extension on the rear face that the NA pulley does not have.

Before you start, yes, I know that we are talking 6 rib vs 8 or 9 rib ( whatever the SRT6 uses ) belt, but in theory the 6 rib belt should work for a test run if the rear sides of the pulleys line up, which they didn't.

The object of this exercise was to see if a 25% underdrive using a lightweight aluminum pulley would both give you 2 or 3 extra HP, while at the same time keep the voltage at @ 14 v even at the 25% reduced speed.
This is about 5,600 RPM alternator speed at 60 MPH as opposed to OEM 7500 RPM )
( in theory, there is enough slack in the current belt tensioner to accommodate the pulley size increase. )

Chris thought maybe we could get a batch made up that would be in the range of $60 - $70 IF this worked, but that is all shelved now that we could not do the experiment.

As a side note : If anyone has an old alternator pulley from an NA, if you could send it to me or Chris, he said he would see about getting a prototype 65 mm aluminum 6 rib pulley made and we could try again.